ROX-17723: Fix imagePullSecret value source

[kurlov]

Description

This fix stage deployment

Checklist (Definition of Done)

- [ ] Unit and integration tests added

• Added test description under Test manual
  - [ ] Documentation added if necessary (i.e. changes to dev setup, test execution, ...)
• CI and all relevant tests are passing
• Add the ticket number to the PR title if available, i.e. ROX-12345: ...
  - [ ] Discussed security and business related topics privately. Will move any security and business related topics that arise to private communication channel.
  - [ ] Add secret to app-interface Vault or Secrets Manager if necessary
  - [ ] RDS changes were e2e tested manually
  - [ ] Check AWS limits are reasonable for changes provisioning new resources

Test manual

HELM_DRY_RUN=true HELM_DEBUG=true AWS_SAML_ROLE=<stage user> ./terraform_cluster.sh stage <stage_cluster>

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kurlov, SimonBaeumer

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [SimonBaeumer,kurlov]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment